The present invention relates to a thin-film electron emitter device which has an electron emission area of three layer structure of a base electrode, an insulator and a top electrode to emit electrons from the top electrode into a vacuum, and also to a display apparatus using the electron emitter device.
One of display apparatuses which use a cold cathode array having cold cathodes arranged at intersections of a group of electrodes perpendicular to each other, is such a field emission display (FED) as disclosed, e.g., in JP-A-4-289644 (laid open on Oct. 14, 1992) corresponding to U.S. Ser. No. 5,908,70 filed on Oct. 1, 1990 (assignee: Raytheon Company). The FED, which has a multiplicity of field emitters arranged at pixels, acts to accelerate field electrons emitted from the emitters in a vacuum and to direct them to phosphors for luminescence.
Meanwhile, a thin-film electron emitter device acts to emit hot electrons generated in an insulator from a surface of a top electrode into a vacuum by a voltage applied between a top electrode and base electrode of a three layer structure including the base electrode, insulator and top electrode. The thin-film electron emitter devices include an MIM (metal-insulator-metal) electron emitter device in which top and base electrodes are made of metals and an MIS (metal-insulator-semiconductor) electron emitter device in which at least one of the top and base electrodes is made of semiconductor. One of the MIM electron emitter devices is disclosed, e.g., in JP-A-7-65710 (laid open on Mar. 10, 1995). Included in other known types of electron emitter devices are a device wherein an insulating film, an insulator and a semiconductor film are laminated in this order, a device wherein the above lamination order is made reversed, a device wherein the semiconductor film is made of porous semiconductor, and a device wherein an upper surface of the porous semiconductor is oxidized. In the thin-film electron emitter devices of various types of insulator structures, the insulator acts as an electron accelerating layer.
When compared to the field emitter used in the FED, the thin-film electron emitter device has characteristics preferable in a display apparatus such as a high surface contamination resistance and a low driving voltage. However, the prior art thin-film electron emitter device has had problems that it is short in life because concentration of a field in the insulator at the edge of the device causes its breakdown and that formation of such a thin-film electron emitter device into a matrix causes uneven distribution of the amount of emitted electrons on a plane. In order to solve these problems, we proposed a structure of a thin-film electron emitter device in which a thick field insulator for preventing field concentration of the insulator at its ends and a top electrode busline for reducing a wiring resistance of a top electrode are provided to provide a long operating life and a uniform in-plane electron emission distribution, and also proposed a method for manufacturing the emitter device, in Japanese Patent Application No. 8-250279 (JP-A-10-92299 laid open on Apr. 10, 1998) filed on Sep. 20, 1996.
This structure is featured in that the top electrode is deposited so as to cover the top electrode busline layer to form a laminated top electrode busline. When such a structure that the top electrode is finally formed, is employed, process damage of the insulator can be prevented or recovered, thus enabling fabrication of a thin-film electron emitter device having a high reliability. Further it is possible to form the top electrode busline on the field insulator and to form the top electrode on the insulator in a self-alignment relation.
When it is desired to manufacture a large-size display apparatus, this involves a problem of increased wiring resistance. For this reason, the top electrode busline is made as thick as possible. However, when the top electrode busline is made too thick, this causes a step at ends of the top electrode busline to become sharp, whereby the top electrode to be formed on the top electrode busline tends to be easily broken and disconnected at the step parts and to generate a failure.
It is therefore an object of the present invention to provide a thin-film electron emitter device of a structure wherein reliable electric connection between a top electrode and a top electrode busline can be established, and also to provide a display apparatus using such a device.
In accordance with an aspect of the present invention, a top electrode busline made thin on its connection side with a top electrode is formed on a field insulator thicker than an insulator and formed around the insulator forming electron emission areas, and the top electrode covers the top electrode busline to be connected with thin areas thereof.